For a company that has made headlines for its progressive critique of the fashion industry—decrying unrealistic Photoshopping, restrictive sizing, and model fetishizing—ModCloth’s financial district office is disarmingly retro. Stepping off the elevator into the ninth-floor workspace feels a bit like entering a teenage girl’s bedroom. Spiraling clothespin art adorns the reception area, its couches strewn with knit throws and embroidered pillows. The desks are dotted with dried flowers, Nicolas Cage tear-outs, photo strips, and an inflatable My Little Pony crowned with a lopsided tiara. A nearby shelf is stacked with classic board games. Images of pigeon-toed girls in hourglass frocks and high-waisted bikinis are displayed alongside framed snapshots of a glasses-wearing pug named Winston—the company’s unofficial mascot.

This is the pop-playing headquarters of ModCloth cofounder Susan Gregg Koger’s $150 million e-retail apparel brand. But what started out as an excuse to shill patent leather Mary Janes and rhinestone costume jewelry has grown into a groundbreaking body image movement. The fourth-wave feminist revolution is here—it just happens to be peddling animal puns and sweetheart dresses along with female empowerment.

Koger, 31, founded the site with her boyfriend turned husband, Eric Koger, in 2002, as a freshman at Carnegie Mellon hoping to make a little extra cash off her vintage finds. The ModCloth site was modeled off her own wardrobe—often described as quirky or, less kindly, twee. The lithe, bare-faced brunette with a pixie cut is fond of Peter Pan collars, fit-and-flare dresses, oversize buttons, cardigans, bows, and costume jewelry. And the prints—oh, the prints: A scan of ModCloth’s offerings reveals dresses liberally patterned in pies, books, kittens, owls, ice cream cones, unicorns, telephones, and cocktails—each with a punny name to match (Weekend Fore-cats dress, $99.99). The brand’s unabashed embrace of cuteness and quirk has garnered it a fair share of mockery. (In a post titled “The 10 Most ModCloth Items at ModCloth,” Jezebel contributor Laura Beck memorably fantasized about living inside the site, “adorably trapped for eternity, doing fashion shows for bunnies in onesies and ponies in corsets.”) Koger is wearily diplomatic in defense of her vision. “The ModCloth girl is coming to us to find pretty, feminine looks that express who she is,” she says. “And yeah, sometimes that’s expressing her love of cats or birds.”

After college, the couple expanded the scope of the site from pure vintage into wholesale pieces from independent brands. The modern-day Bettie Page vibe quickly gained a following, and the site secured its first round of outside funding in 2008. After the brand netted $15.6 million in 2009, Inc. named ModCloth America’s fastest-growing retailer, putting it in the ranks of cash-flush e-commerce sites like Asos, Net-a-Porter, and Nasty Gal. ModCloth swag has been worn by a squad of aspirational celebrity besties, including Taylor Swift, Mindy Kaling, Amy Schumer, Laverne Cox, and Meghan Trainor; indie ingenue Zooey Deschanel might as well be the brand’s patron saint.

Today, the e-commerce site, headquartered on Sansome Street, stocks more than 700 indie labels and nets five million visitors each month. After two rounds of layoffs in 2014, the company is now profitable, with a net-revenue growth of more than 50 percent in the past two years, according to ModCloth. In January, Urban Outfitters’ former chief strategy officer, Matthew Kaness, became the new chief executive officer, replacing Eric Koger.

It seems counterintuitive that a retailer best known for ’50s-housewife silhouettes would be a leading force in the body-positive movement. But over the years, Koger has increasingly used the brand as a social platform. “Fashion is great. I think the transformative power of an outfit is amazing,” she says. “But this is my life’s work—I’ve always aspired to a deeper message.” From the beginning, she has avoided hiring professional models, instead enlisting friends, employees, and loyal customers for ad campaigns. In 2012, ModCloth launched the Style Gallery feature, which allows shoppers to upload photos of themselves and their sizing details alongside product reviews. Since then, over 71,000 outfit photos have been shared. Two-thirds of the site’s product reviews include body measurements.

Last year, the company became the first retailer to back the federal Truth in Advertising Act, pledging not to use Photoshop in its marketing. “It’s something that we had been doing a long time that we wanted to be louder and prouder about,” says Koger. “To me, aspirational style is about being confident and self-assured—not about having a specific body type.” In February, nine ModCloth employees of all sizes, Koger included, stripped down to bikinis and one-pieces to advertise a swimwear collection inspired by Golden Age actress and competitive swimmer Esther Williams. Transgender comedian Rye Silverman was a featured model in ModCloth’s #FashionTruth campaign in April, when Koger named a plaid halter dress, the All About Rye, after her. “Our ad campaigns set us apart aesthetically and let us connect emotionally,” says Koger. She refers to the “ModCloth girl” as if she’s a close friend, spouting off autobiographical stats—“Her average age is 27, maybe she’s just finished grad school”—and taste preferences.

Koger has been a vocal advocate for challenging sizing ideals, having introduced styles in sizes 16 and up on the site in 2013. “If you look at the statistics, the average woman is a size 14,” she says. “We realized how crazy underserved that market is.” In August, she put her money where her mouth is when she launched an in-house ModCloth label, which offers 95 percent of its styles in sizes XS to 4X. The collection debuted at the company’s pop-up Fit Shop on Grant Avenue, ModCloth’s first foray into brick and mortar. The store is an art-directed ModCloth dream world, where string lights and pennants hang from pressed-tin ceilings, mismatched area rugs cover the wood floors, and ModStylists in clear-frame glasses, high-waisted skirts, and T-strap heels offer one-on-one appointments. Fresh from a scouting trip to Paris, clad in a striped sweater layered over a polka-dot button-down, Koger recently flipped through plaid dresses, pussy-bow blouses, and belted skirts on the Fit Shop racks. She paused to admire the Selfie Station, where shoppers of various sizes have posted photos of themselves modeling the same looks. (“We want every moment to be Instagrammable,” she says.)

Much of ModCloth’s first collection sold out in two weeks, and the Fit Shop, which was originally intended to be a three-week experiment, has been extended through the end of the year. While orders placed at the Fit Shop are still filled through the website, that won’t be the case for long: Koger is scouting locations for ModCloth’s first permanent storefront, set to open next year.

Thirteen years after selling her first vintage frock online, Koger is poised for the big time, with plans to quadruple business in the next five years. “When I started doing this, I was 17,” she says, snapping an iPhone photo of the Fit Shop’s window dressing. “As the company has grown up, the ModCloth girl has grown up—she’s ready to explore.”